The present invention relates to a liquid ejecting apparatus which ejects a liquid, supplied from a liquid cartridge and the like, in the form of liquid droplets, and particularly to a liquid ejecting apparatus which enables a high speed printing by realizing a reduction in its size while increasing the number of nozzles of an ejecting head.
As one kind of liquid ejecting apparatus, there is an inkjet recording apparatus. Such an inkjet recording apparatus has advantages of, as well as being able to print directly on a recording medium, being easy to reduce the size of a head, and furthermore that a color printing can also be easily carried out by changing ink colors.
FIG. 8 is one representative example of an ejecting head used for the recording apparatus described heretofore. The ejecting head includes a head casing 76, in which a piezoelectric vibrator 74 serving as pressure generating means is stored, and a flow channel unit 86, which is fixed to a unit fixation surface of the head casing 76 by an adhesive or the like.
The flow channel unit 86 is formed by laminating a flow channel formation substrate 71 formed with a flow channel space including a pressure generating chamber 79, a nozzle plate 70 being laminated to one surface of the flow channel formation substrate 71 and being formed with a nozzle orifice 75 which ejects the ink in the pressure generating chamber 79, and a vibration plate (sealing plate) 72 being laminated to the other surface of the flow channel formation substrate 71 and sealing the flow channel space including the pressure generating chamber 79.
In the nozzle plate 70, a nozzle array 85 is formed by arraying a plurality of the nozzle orifices 75, in this example, two nozzle arrays 85 are formed, each being configured to eject a different kind of ink. The nozzle plate 70 is formed from a stainless steel plate. The pressure generating chambers 79 in communication with each of the nozzle orifices 75 are arranged in the flow channel formation substrate 71. The vibration plate 72 is formed by laminating a stainless steel plate to a polyphenylene sulfide film. The stainless steel plate is etched away to leave necessary portions, thereby forming an island portion (not shown).
The flow channel unit 86 is formed by laminating the nozzle plate 70 to one surface of the flow channel formation substrate 71, and by laminating the vibration plate 72 to the other surface with the island portion disposed on the outer side.
In contrast, the head casing 76, being formed by injection molding a thermosetting resin or a thermoplastic resin, is formed with a storage space 81 penetrating vertically and extending along the nozzle array 85. Also, the unit fixation surface of the head casing 76 is formed with a common ink reservoir 77 communicating with each pressure generating chamber 79 and storing ink to be supplied to each pressure generating chamber 79. Furthermore, the head casing 76 is formed with an ink supply path 78 which supplies the ink reservoir 77 with the ink introduced from a filter unit 88.
Also, a vibrator unit 91 is formed by arranging the bar-like piezoelectric vibrators 74 on the leading end side of a stationary plate 80, and connecting a flexible cable 82 for inputting an ejecting signal to each piezoelectric vibrator 74. The piezoelectric vibrators 74 have longitudinal vibration mode.
The vibrator unit 91 is stored in the storage space 81 of the head casing 76 with the leading end of each piezoelectric vibrator 74 projecting from the unit fixation surface, and the vibration plate 72 of the flow channel unit 86 is bonded by the adhesive to the unit fixation surface of the head casing 76. In this condition, the leading end face of the piezoelectric vibrator 74 is fixed to the island portion of the vibration plate 72, and the stationary plate 80 is adhesively fixed to the head casing 76.
A head substrate 87 is disposed on a side of the head casing 76 opposite the unit fixation surface and, furthermore, the filter unit 88 is attached to the head substrate 87, thereby forming the ejecting head 100.
A hollow ink introduction needle 90, which is supplied with the ink from a not-shown ink cartridge and the like, stands on the filter unit 88, and a filter 89 which filters ink is provided in a root portion of the ink introduction needle 90. In the figure, a seal member 94 seals an ink supply opening 95 of the filter unit 88 and an ink supply path 78 of the head casing 76 so as to maintain a liquid-tightness therebetween.
Flanges 92b, each of which an attachment hole 93b for attaching the ejecting head 100 to a not-shown carriage and the like is bored in, are formed at both side portions of the filter unit 88. Similarly, flanges 92a, each of which an attachment hole 93a is bored in, are also formed at both side portions of the head casing 76. The holes and flanges function as attachment holes 93 and flanges 92 which are integrated and stacked one on the other in an assembled condition.
In the ejecting head 100 of the configuration described heretofore, the piezoelectric vibrator 74 is extended and contracted in a longitudinal direction thereof by inputting a drive signal generated by a not-shown drive circuit to the piezoelectric vibrator 74 via the flexible cable 82. The ejecting head 100 is configured in such a way that the island portion of the vibration plate 72 is vibrated by the extension and contraction of the piezoelectric vibrator 74 to vary a pressure in the pressure generating chamber 79, thereby ejecting the ink in the pressure generating chamber 79 from the nozzle orifice 75 as ink droplets.
At this point, as an inkjet recording apparatus having head chips staggered, one shown in JP-A-2002-127377 is disclosed.
In recent years, in order to realize a high speed printing, an increase in the number of nozzles of the ejecting head 100 has been considered. However, when intending to increase the number of nozzles of one ejecting head 100, each part, such as the nozzle plate 70, the flow channel formation substrate 71 and the vibrator unit 91, which form the ejecting head, has to be increased in size. When each part is thus increased in size, it becomes difficult to maintain a high processing accuracy, and processing equipment has to be subjected to an overhaul in order to carry out a processing with high accuracy. Moreover, when intending to fabricate large-size parts with high accuracy, a significant reduction even in yield cannot be avoided. Consequently, an increase in the size of parts results in an extreme increase in cost, constituting a limitation realistically.
At this point, it has been considered that one head unit 101 is formed by arranging a plurality of the ejecting heads 100 described heretofore, thereby increasing the number of nozzles of the one head unit 101.
FIG. 9 shows an example of the head unit 101 formed by arranging a plurality of the ejecting heads 100. In this example, the unit head 101 is formed by arranging two ejecting heads 100, each having two nozzle arrays 85, in a main scanning direction X. Then, two ejecting heads 100a and 100b are positioned in such an offset manner that a nozzle array 85 end downstream of one ejecting head 100a in a paper transport direction (a Y direction) is aligned with a nozzle array 85 end upstream of the other ejecting head 100b in the paper transport direction (Y direction).
Such a head unit 101, being mounted on the not-shown carriage, reciprocates in the main scanning direction X, and ejects ink droplets from the nozzle orifices 75 forming each nozzle array 85 while transporting a recording medium toward a sub-scanning direction Y, thereby forming an image on the recording medium using a dot matrix.
When the plurality of ejecting heads 100 are thus arranged, since the flange 92 and the like which are attachment members for attaching ejecting head 100 are formed for each ejecting head 100, some distance is required between the ejecting heads 100, providing a so-called dead space, which leads to an increase in the size of the head unit 101 itself, thereby increasing the size of the recording apparatus itself.
Moreover, the plurality of ejecting heads 100 need to be positioned with accuracy. Particularly, as a relative displacement of the two ejecting heads 100 in the Y direction, which is the paper transport direction, cannot be electrically corrected, their physical attachment positions need to be determined with high accuracy. Consequently, there has been the problem wherein an accurate physical positioning operation has to be carried out each time each ejecting head 100 is attached.